Conductive compositions and processes for use in the manufacture of semiconductor devices—organic medium components

ABSTRACT

Embodiments of the invention relate to a silicon semiconductor device, and a conductive paste for use in the front side of a solar cell device.

FIELD OF THE INVENTION

Embodiments of the invention relate to a silicon semiconductor device,and a conductive paste for use in the front side of a solar cell device.

TECHNICAL BACKGROUND OF THE INVENTION

A conventional solar cell structure with a p-type base has a negativeelectrode that is typically on the front-side or sun side of the celland a positive electrode on the backside. It is well-known thatradiation of an appropriate wavelength falling on a p-n junction of asemiconductor body serves as a source of external energy to generatehole-electron pairs in that body. Because of the potential differencewhich exists at a p-n junction, holes and electrons move across thejunction in opposite directions and thereby give rise to flow of anelectric current that is capable of delivering power to an externalcircuit. Most solar cells are in the form of a silicon wafer that hasbeen metalized, i.e., provided with metal contacts that are electricallyconductive.

Electrode of solar cell is usually formed by applying a conductive pasteonto a substrate and firing it. Conductive paste is applied onto thesurface of solar cell and the paste is fired for sintering. Pastetypically contains (a) conductive power such as silver or aluminum, (b)glass frit as inorganic binder, (c) organic medium and (d) optionaladditive.

U.S. Pat. No. 7,494,607 discloses conventional organic mediums includingethylhydroxyethyl cellulose, wood rosin, mixtures of ethyl cellulose andphenolic resins, polymethacrylates of lower alcohols, monobutyl ether ofethylene glycol monoacetate ester alcohols and terpenes such as alpha-or beta-terpineol or mixtures thereof with other solvents such askerosene, dibutylphthalate, butyl carbitol, butyl carbitol acetate,hexylene glycol and high boiling alcohols and alcohol esters.

Although various methods and compositions for forming solar cells exist,there is a need for compositions, structures, and devices which haveimproved electrical performance, adhesion properties, and methods ofmaking.

SUMMARY OF THE INVENTION

An embodiment of the present invention relates to a thick filmconductive composition comprising:

-   (a) one or more electrically conductive powders;-   (b) one or more glass frits; dispersed in-   (c) organic medium selected from the group consisting of:    Bis(2-(2Butoxyethoxy) Ethyl) Adipate, dibasic ester, Octyl Epoxy    Tallate, isotetradecanol, and pentaerythritol ester of hydrogenated    rosin.

In an aspect of the embodiment, the glass frit may comprise, based onweight percent of total glass composition: SiO₂ 1-36, Al₂O₃ 0-7, B₂O₃1.5-19, PbO 20-83, ZnO 0-42, CuO 0-4, Bi₂O₃ 0-35, ZrO₂ 0-8, TiO₂ 0-7,PbF₂ 3-34.

In an embodiment, the composition may further comprise an additive. Inan aspect, the additive may be a metal/metal oxide additive selectedfrom (a) a metal wherein said metal is selected from Zn, Mg, Gd, Ce, Zr,Ti, Mn, Sn, Ru, Co, Fe, Cu, and Cr; (b) a metal oxide of one or more ofthe metals selected from Zn, Mg, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cuand Cr; (c) any compounds that can generate the metal oxides of (b) uponfiring; and (d) mixtures thereof. In an aspect of the embodiment, theZn-containing additive is ZnO.

An embodiment of the invention relates to a structure, wherein thestructure comprises the thick film composition and a substrate. Thesubstrate may be one or more insulating layers. The substrate may be oneor more semiconductor substrates. In an aspect, the thick filmcomposition may be formed on the one or more insulating layers. In anaspect, the one or more insulating layers may be formed on asemiconductor substrate. In a further aspect, upon firing, the organicvehicle is removed and the silver and glass frits are sintered.

In an embodiment of the invention, an electrode is formed from thecomposition, and said composition has been fired to remove the organicvehicle and sinter the glass particles.

An embodiment of the invention relates to a method of manufacturing asemiconductor device. The method comprises the steps of:

-   (a) providing one or more semiconductor substrates, one or more    insulating films, and a thick film composition, wherein the thick    film composition comprises: a) one or more electrically conductive    powders, b) one or more glass frits, dispersed in c) an organic    medium selected from the group consisting of:    Bis(2-(2Butoxyethoxy)Ethyl) Adipate, dibasic ester, Octyl Epoxy    Tallate, isotetradecanol, and pentaerythritol ester of hydrogenated    rosin,-   (b) applying the insulating film on the semiconductor substrate,-   (c) applying the thick film composition on the insulating film on    the semiconductor substrate, and-   (d) firing the semiconductor, insulating film and thick film    composition, wherein, upon firing, the organic vehicle is removed,    the silver and glass frits are sintered, and the insulating film is    penetrated by components of the thick film composition.

In an aspect of the embodiment, the insulating film comprises one ormore components selected from: titanium oxide, silicon nitride, SiNx:H,silicon oxide, and silicon oxide/titanium oxide.

A further embodiment relates to structures including the thick filmconductive composition. The structure may include an insulating layer.The structure may include a semiconductor substrate. An aspect of thepresent invention relates to semiconductor devices that contain thestructure. An aspect of the present invention relates to photovoltaicdevices that contain the structure. An aspect of the present inventionrelates to solar cells that contain the structure. An aspect of thepresent invention relates to solar panels that contain the structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram illustrating the fabrication of asemiconductor device.

Reference numerals shown in FIG. 1 are explained below.

-   -   10: p-type silicon substrate    -   20: n-type diffusion layer    -   30: silicon nitride film, titanium oxide film, or silicon oxide        film    -   40: p+ layer (back surface field, BSF)    -   60: aluminum paste formed on backside    -   61: aluminum back electrode (obtained by firing back side        aluminum paste)    -   70: silver or silver/aluminum paste formed on backside    -   71: silver or silver/aluminum back electrode (obtained by firing        back side silver paste)    -   500: silver paste formed on front side according to the        invention    -   501: silver front electrode according to the invention (formed        by firing front side silver paste)

FIG. 2A provides a top side view of an exemplary semiconductor in whichthe thick film conductor composition has been printed on the substrateto form two busbars.

FIG. 2B provides a top side view of an exemplary semiconductor in whichthe thick film conductor composition has been printed on the substrateto form three busbars.

FIG. 3 illustrates the % efficiency for 200 μm wide lines withcomposition A0, and B1 to B9, described herein.

FIG. 4 illustrates the % efficiency for 100 micron lines withcompositions described herein.

FIG. 5 illustrates the % efficiency for 200 μm wide lines withcompositions described herein.

DETAILED DESCRIPTION OF THE INVENTION

The present invention addresses the need for semiconductor compositionswith improved electrical performance, semiconductor devices, methods ofmanufacturing the semiconductor devices, and the like.

An embodiment of the present invention relates to thick film conductorcompositions. In an aspect of the embodiment, the thick film conductorcompositions may include: a conductive powder, a flux material, and anorganic medium. The flux material may be glass frit or mixture of glassfrits. The organic medium may include one or more components selectedfrom the group consisting of: Bis(2-(2Butoxyethoxy)Ethyl) Adipate,dibasic ester such as DBE, DBE-2, DBE-3, DBE-4, DBE-5, DBE-6, DBE-9,DBE-IB (DBE series are different in terms of mixed ratio of components),Octyl Epoxy Tallate [DRAPEX (R) 4.4] from Witco Chemical, and Oxocol(isotetradecanol made by Nissan Chemical) and Foralyn™ 110(pentaerythritol ester of hydrogenated rosin from Eastman Chemical BV).The thick film conductor compositions may also include an additive. Thethick film conductor compositions may include additional additives orcomponents.

An embodiment of the present invention relates to structures, whereinthe structures include the thick film conductor compositions. In anaspect, the structure also includes one or more insulating films. In anaspect, the structure does not include an insulating film. In an aspect,the structure includes a semiconductor substrate. In an aspect, thethick film conductor composition may be formed on the one or moreinsulating films. In an aspect, the thick film conductor composition maybe formed on the semiconductor substrate. In the aspect wherein thethick film conductor composition may be formed on the semiconductorsubstrate, the structure may not contain an applied insulating film.

In an embodiment, the thick film conductor composition may be printed onthe substrate to form busbars. The busbars may be more than two busbars.For example, the busbars may be three or more busbars. In addition tobusbars, the thick film conductor composition may be printed on thesubstrate to form connecting lines. The connecting lines may contact abusbar. The connecting lines contacting a busbar may be interdigitatedbetween the connecting lines contacting a second busbar.

In an exemplary embodiment, three busbars may be parallel to each otheron a substrate. The busbars may be rectangular in shape. Each of thesides of the middle busbar may be in contact with connecting lines. Oneach of the side busbars, only one side of the rectangle may be incontact with connecting lines. The connecting lines contacting the sidebusbars may interdigitate with the connecting lines contacting themiddle busbar. For example, the connecting lines contacting one sidebusbar may interdigitate with the connecting lines contacting the middlebusbar on one side, and the connecting lines contacting the other sidebusbar may interdigitate with the connecting lines contacting the middlebusbar on the other side of the middle busbar.

FIG. 2A provides an exemplary representation of an embodiment in whichthere are two busbars. A first busbar 201 is in contact with a first setof connecting lines 203. A second busbar 205 is in contact with a secondset of connecting lines 207. The first set of connecting lines 203interdigitate with the second set of connecting lines 207.

FIG. 2B provides an exemplary representation of an embodiment in whichthere are three busbars. A first busbar 209 is in contact with a firstset of connecting lines 211. A second busbar 213 is in contact with botha second set of connecting lines 215 and a third set of connecting lines217. The second set of connecting lines 215 contacts one side of thesecond busbar 213; the third set of connecting lines 217 contacts theopposite side of the second busbar 213. A third busbar 219 is in contactwith a fourth set of connecting lines 221. The first set of connectinglines 211 interdigitate with the second set of connecting lines 215. Thethird set of connecting lines 217 interdigitate with the fourth set ofconnecting lines 221.

In an embodiment, the busbar formed on the substrate may consist of twobusbars arrayed in a parallel arrangement with conductor lines formedperpendicular to the busbar and arrayed in an interdigitated parallelline pattern. Alternately, the busbars may be three or more busbars. Inthe case of three busbars, the central busbar may serve as a commonbetween the busbars to each side in a parallel arrangement. In thisembodiment, the area coverage of the three busbars may be adjusted toapproximately the same as the case for the use of two busbars. In thecase of three busbars, the perpendicular lines are adjusted to shorterdimensions appropriate to the spacing between pairs of busbars.

In an embodiment, the components of the thick film conductorcomposition(s) are electrically functional silver powders, one or moreadditive(s), and a glass frit dispersed in an organic medium, whereinthe organic medium comprises one or more components selected from thegroup consisting of: Bis(2-(2Butoxyethoxy)Ethyl) Adipate, DBE, DBE-2,DBE-3, DBE-4, DBE-5, DBE-6, DBE-9, DBE-IB, Octyl Epoxy Tallate [DRAPEX(R) 4.4] from Witco Chemical, and Oxocol (isotetradecanol made by NissanChemical) and Foralyn™ 110 (pentaerythritol ester of hydrogenated rosinfrom Eastman Chemical BV). The glass frit may be lead-free. Additionaladditives may include metals, metal oxides or any compounds that cangenerate these metal oxides during firing. The components are discussedherein below.

I. Inorganic Components

An embodiment of the present invention relates to thick film conductorcompositions. In an aspect of the embodiment, the thick film conductorcompositions may include: a conductive material, a flux material, and anorganic medium. The conductive material may include silver. In anembodiment, the conductive material may be a conductive powder. The fluxmaterial may include a glass frit or glass frits. The glass frit may belead-free. The thick film conductor compositions may also include anadditive. The additive may be a metal/metal oxide additive selected from(a) a metal wherein said metal is selected from Zn, Mg, Gd, Ce, Zr, Ti,Mn, Sn, Ru, Co, Fe, Cu and Cr; (b) a metal oxide of one or more of themetals selected from Zn, Mg, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu andCr; (c) any compounds that can generate the metal oxides of (b) uponfiring; and (d) mixtures thereof. The thick film conductor compositionsmay include additional components.

As used herein, “busbars” means a common connection used for collectionof electrical current. In an embodiment, the busbars may be rectangularshaped. In an embodiment, the busbars may be parallel.

As used herein, “flux material” means a substance used to promotefusion, or a substance that fuses. In an embodiment, the fusion may beat or below required process temperatures to form a liquid phase.

In an embodiment, the inorganic components of the present inventioncomprise (1) electrically functional silver powders; (2) glass frit; andoptionally (3) one or more metal/metal oxide additive selected from (a)a metal wherein said metal is selected from Zn, Mg, Gd, Ce, Zr, Ti, Mn,Sn, Ru, Co, Fe, Cu and Cr; (b) a metal oxide of one or more of themetals selected from Zn, Mg, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu andCr; (c) any compounds that can generate the metal oxides of (b) uponfiring; and (d) mixtures thereof. In an embodiment, the glass frit maybe lead-free.

A. Electrically Conductive Functional Materials

Electrically conductive materials may include Ag, Cu, Pd, and mixturesthereof. In an embodiment, the electrically conductive particle is Ag.However, these embodiments are intended to be non-limiting. Embodimentsin which other conductive materials are utilized are contemplated andencompassed.

The silver may be in a particle form, a powder form, a flake form,spherical form, provided in a colloidal suspension, a mixture thereof,etc. The silver may be silver metal, alloys of silver, or mixturesthereof, for example. The silver may include silver oxide (Ag₂O) orsilver salts such as AgCl, AgNO₃, or AgOOCCH₃ (silver acetate), silverorthophosphate, Ag₃PO₄, or mixtures thereof, for example. Any form ofsilver compatible with the other thick film components may be used, andwill be recognized by one of skill in the art.

The silver may be any of a variety of percentages of the composition ofthe thick film composition. In a non-limiting embodiment, the silver maybe from about 70 to about 99 wt % of the solid components of the thickfilm composition. In a further embodiment, the silver may be from about70 to about 85 wt % of the solid components of the thick filmcomposition. In a further embodiment, the silver may be from about 90 toabout 99 wt % of the solid components of the thick film composition.

In an embodiment, the solids portion of the thick film composition mayinclude about 80 to about 90 wt % silver particles and about 0 to about100 wt %, for example 0 to 50 wt %, 0 to 20 wt % silver flakes. In anembodiment, the solids portion of the thick film composition may includeabout 50 to about 90 wt % silver particles and about 0 to about 10 wt %silver flakes. In another embodiment, the solids portion of the thickfilm composition may include about 75 to about 90 wt % silver flakes andabout 1 to about 10 wt % of colloidal silver. In a further embodiment,the solids portion of the thick film composition may include about 60 toabout 90 wt % of silver powder or silver flakes and about 0.1 to about20 wt % of colloidal silver.

In an embodiment, a thick film composition includes a functional phasethat imparts appropriate electrically functional properties to thecomposition. The functional phase may include electrically functionalpowders dispersed in an organic medium that acts as a carrier for thefunctional phase that forms the composition. In an embodiment, thecomposition may be applied to a substrate. In a further embodiment, thecomposition and substrate may be fired to burn out the organic phase,activate the inorganic binder phase and to impart the electricallyfunctional properties.

In an embodiment, the functional phase of the composition may be coatedor uncoated silver particles which are electrically conductive. In anembodiment, the silver particles may be coated. In an embodiment, thesilver may be coated with various materials such as phosphorus. In anembodiment, the silver particles may be at least partially coated with asurfactant. The surfactant may be selected from, but is not limited to,stearic acid, palmitic acid, a salt of stearate, a salt of palmitate andmixtures thereof. Other surfactants may be utilized including lauricacid, palmitic acid, oleic acid, stearic acid, capric acid, myristicacid and linolic acid. The counter-ion can be, but is not limited to,hydrogen, ammonium, sodium, potassium and mixtures thereof.

The particle size of the silver is not subject to any particularlimitation. In an embodiment, an average particle size is less than 10microns; in a further embodiment, the average particle size is less than5 microns. In an embodiment, the average particle size may be from 0.1to 5 microns.

In an embodiment, silver oxide may be dissolved in the glass during theglass melting/manufacturing process.

B. Additive(s)

An embodiment of the present invention relates to thick filmcompositions which contain one or more additive. In an aspect of thisembodiment, the additive may be a metal/metal oxide additive selectedfrom (a) a metal wherein said metal is selected from Zn, Mg, Gd, Ce, Zr,Ti, Mn, Sn, Ru, Co, Fe, Cu and Cr; (b) a metal oxide of one or more ofthe metals selected from Zn, Mg, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cuand Cr; (c) any compounds that can generate the metal oxides of (b) uponfiring; and (d) mixtures thereof.

In an embodiment, the particle size of the additives is not subject toany particular limitation. In an embodiment, an average particle sizemay be less than 10 microns; in an embodiment, an average particle sizemay be less than 5 microns. In an embodiment, the average particle sizemay be from 0.1 to 1.7 microns. In a further embodiment, the averageparticle size may be from 0.6 to 1.3 microns. In an embodiment, theaverage particle size may be from 7 to 100 nm. In a further embodiment,the particle size of the additives can be at the atomic or molecularlevel when an organo-metallic compound such as a metal resinate is used.

In an embodiment, the particle size of the metal/metal oxide additivemay be in the range of 7 nanometers (nm) to 125 nm. In an embodiment,the particle size of the metal/metal oxide additive may be in the rangeof 7 nanometers (nm) to 100 nm. In an embodiment, MnO₂ and TiO₂ may beutilized in the present invention with an average particle size range(d₅₀) of 7 nanometers (nm) to 125 nm. In a further embodiment, theparticle size of the additives can be at the atomic or molecular levelwhen an organo-metallic compound such as a metal resinate is used.

In an embodiment, the additional additive may be a Zn-containingadditive. The Zn-containing additive may, for example be selected from(a) Zn, (b) metal oxides of Zn, (c) any compounds that can generatemetal oxides of Zn upon firing, and (d) mixtures thereof.

In one embodiment, the Zn-containing additive is ZnO, wherein the ZnOmay have an average particle size in the range of 10 nanometers to 10microns. In a further embodiment, the ZnO may have an average particlesize of 40 nanometers to 5 microns. In still a further embodiment, theZnO may have an average particle size of 60 nanometers to 3 microns. Ina further embodiment, the Zn-containing additive may have an averageparticle size of less than 0.1 μm. In particular the Zn-containingadditive may have an average particle size in the range of 7 nanometersto less than 100 nanometers.

In a further embodiment the Zn-containing additive (for example Zn, Znresinate, etc.) may be present in the total thick film composition inthe range of 2 to 16 weight percent. In a further embodiment theZn-containing additive may be present in the range of 4 to 12 weightpercent total composition. In an embodiment, ZnO may be present in thecomposition in the range of 2 to 10 weight percent total composition. Inan embodiment, the ZnO may be present in the range of 4 to 8 weightpercent total composition. In still a further embodiment, the ZnO may bepresent in the range of 5 to 7 weight percent total composition.

In an embodiment, the additional additive may be a Mg-containingadditive. The Mg-containing additive may, for example be selected from(a) Mg, (b) metal oxides of Mg, (c) any compounds that can generatemetal oxides of Mg upon firing, and (d) mixtures thereof.

In one embodiment, the Mg-containing additive is MgO, wherein the MgOmay have an average particle size in the range of 10 nanometers to 10microns. In a further embodiment, the MgO may have an average particlesize of 40 nanometers to 5 microns. In still a further embodiment, theMgO may have an average particle size of 60 nanometers to 3 microns. Ina further embodiment, the MgO may have an average particle size of 0.1to 1.7 microns. In a further embodiment, the MgO may have an averageparticle size of 0.3 to 1.3 microns. In a further embodiment, theMg-containing additive may have an average particle size of less than0.1 μm. In particular the Mg-containing additive may have an averageparticle size in the range of 7 nanometers to less than 100 nanometers.

MgO may be present in the composition in the range of 0.1 to 10 weightpercent total composition. In one embodiment, the MgO may be present inthe range of 0.5 to 5 weight percent total composition. In still afurther embodiment, the MgO may be present in the range of 0.75 to 3weight percent total composition.

In a further embodiment the Mg-containing additive (for example Mg, Mgresinate, MgO, etc.) may be present in the total thick film compositionin the range of 0.1 to 10 weight percent. In a further embodiment theMg-containing additive may be present in the range of 0.5 to 5 weightpercent total composition. In still a further embodiment, theMg-containing additive may be present in the range of 0.75 to 3 weightpercent total composition.

In a further embodiment, the Mg-containing additive may have an averageparticle size of less than 0.1 μm. In particular the Mg-containingadditive may have an average particle size in the range of 7 nanometersto less than 100 nanometers.

In an embodiment, the additive may contain a mixture of additives. Theadditional additive may be a mixture of metal/metal oxide additivesselected from (a) a metal wherein said metal is selected from Zn, Mg,Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu and Cr; (b) a metal oxide of oneor more of the metals selected from Zn, Mg, Gd, Ce, Zr, Ti, Mn, Sn, Ru,Co, Fe, Cu and Cr; (c) any compounds that can generate the metal oxidesof (b) upon firing; and (d) mixtures thereof.

Compounds that can generate metal oxides of Zn, Mg, Gd, Ce, Zr, Ti, Mn,Sn, Ru, Co, Fe, Cu or Cr upon firing include, but are not limited toresinates, octoates, organic functional units, and the like.

In an embodiment, the additional additive may contain a mixture of ZnOand MgO.

C. Glass Frit

In an embodiment of the invention, the thick film composition mayinclude glass materials. In an embodiment, glass materials may includeone or more of three groups of constituents: glass formers, intermediateoxides, and modifiers. Exemplary glass formers may have a high bondcoordination and smaller ionic size; the glass formers may form bridgingcovalent bonds when heated and quenched from a melt. Exemplary glassformers include, but are not limited to: SiO₂, B₂O₃, P₂O₅, V₂O₅, GeO₂etc. Exemplary intermediate oxides include, but are not limited to:TiO₂, Ta₂O₅, Nb₂O₅, ZrO₂, CeO₂, SnO₂, Al₂O₃, HfO₂ and the like.Intermediate oxides may be used to substitute glass formers, asrecognized by one of skill in the art. Exemplary modifiers may have amore ionic nature. The modifiers may affect specific properties; forexample, modifiers may result in reduction of glass viscosity and/ormodification of glass wetting properties, for example. Exemplarymodifiers include, but are not limited to: oxides such as alkali metaloxides, alkaline earth oxides, PbO, CuO, CdO, ZnO, Bi₂O₃, Ag₂O, MoO₃,WO₃ and the like.

In an embodiment, the glass materials may be selected by one of skill inthe art to assist in the at least partial penetration of oxide ornitride insulating layers. As described herein, this at least partialpenetration may lead to the formation of an effective electrical contactto the silicon surface of a photovoltaic device structure. Theformulation components are not limited to glass forming materials.

In an embodiment of the invention, glass frit compositions (glasscompositions) are provided. Non-limiting examples of glass fritcompositions are listed in Table 1 below and described herein.Additional glass frit compositions are contemplated.

It is important to note that the compositions listed in Table 1 are notlimiting, as it is expected that one skilled in glass chemistry couldmake minor substitutions of additional ingredients and not substantiallychange the properties of the glass composition of this invention. Inthis way, 0-3 weight % substitutions of glass formers such as P₂O₅,GeO₂, V₂O₅ maybe used either individually or in combination to achievesimilar performance. It is also possible to substitute one or moreintermediate oxides, such as TiO₂, Ta₂O₅, Nb₂O₅, ZrO₂, CeO₂, SnO₂ forother intermediate oxides (i.e., Al₂O₃, CeO₂, SnO₂) present in a glasscomposition of this invention. It is observed from the data thatgenerally higher SiO₂ content of the glass degrades performance. TheSiO₂ is thought to increase glass viscosity and reduce glass wetting.Although not represented in the Table 1 compositions, glasses with zeroSiO₂ are expected to perform well, as other glass formers such as P₂O₅,GeO₂ etc. may be used to replace the function of low levels of SiO₂. TheCaO, alkaline earth content, can also be partially or fully replaced byother alkaline earth constituents such as SrO, BaO and MgO.

Exemplary, non-limiting glass compositions in weight percent total glasscomposition are shown in Table 1. In an embodiment, glass compositionsmay comprise the following oxide constituents in the compositional rangeof: SiO₂ 1-36, Al₂O₃ 0-7, B₂O₃ 1.5-19, PbO 20-83, ZnO 0-42, CuO 0-4,Bi₂O₃ 0-35, ZrO₂ 0-8, TiO₂ 0-7, PbF2 3-34 in weight percent of totalglass composition. In a further embodiment, the glass composition maycomprise: SiO₂ 20-24, Al₂O₃ 0.2-0.5, B₂O₃ 5-9, PbO 20-55, Bi₂O₃ 0-33,TiO₂ 5-7, BiF₃ 4-22 in weight percent of total glass composition. Thefluoride used in the composition may be sourced from compounds of theavailable composition such as PbF₂, BiF₃, AlF₃ or other such compoundswith appropriate calculations to maintain the same target composition.An example of this calculation equivalency is shown for Glass ID #1 as:SiO₂ 22.08, Al₂O₃ 0.38, PbO 56.44, B₂O₃ 7.49, TiO₂ 5.86, Bi₂O₃ 6.79, F1.66 weight % where the fluorine is expressed as elemental fluorine andassociated oxides. One skilled in the art would readily make theseconversion calculations. In an embodiment, glass compositions may have atotal of PbO, Bi₂O₃ and PbF₂ between 60-70% in wt %. In an embodiment,the glass composition may be generally described by the following inweight % of total glass composition: SiO₂ 1-36, PbO 20-83, B₂O₃ 1.5-19,PbF₂ 4-22 and optional constituents include: Al₂O₃ 0-7, ZrO₂ 0-8, ZnO0-12, CuO 0-4, Bi₂O₃ 0-35, and TiO₂ 0-7. It is also possible to describethe compositional range as a SiO₂, PbO, F, and B₂O₃ with optionaladditions of Al₂O₃, ZrO₂, ZnO, CuO, Bi₂O₃, TiO₂, and compound fluoridesas source compound for the supply of fluorine to the composition.

TABLE 1 Glass Composition(s) in Weight Percent Total Glass CompositionGlass Component (wt % total glass composition) ° C. Density ID# SiO₂Al₂O₃ PbO ZrO₂ B₂O₃ ZnO CuO Bi₂O₃ TiO₂ PbF₂ CdO T_(g) (g/cc) 1 22.080.38 46.68 7.49 6.79 5.86 10.7 510 4.83 2 29.32 3.13 51.55 3.06 2.572.74 7.64 525 4.59 3 14.87 6.56 46.66 14.82 17.1 490 4.47 4 9.5 1.4663.94 13.05 3 9.04 458 5.59 5 1.1 82.7 11.2 5 298 6.2 6 14.64 6.46 30.6314.6 33.7 465 4.61 7 20.94 1.97 25.93 7.95 17.98 10.5 2.05 12.7 503 3.88 21.84 0.38 21.48 7.41 32.5 5.79 10.6 485 4.69 9 21.87 0.38 36.57 7.426.73 5.8 21.2 455 4.81 10 22.14 0.39 53.34 7.51 5.87 10.8 478 4.84 1130.61 2.55 55.02 1.83 2.7 7.29 524 4.63 12 32.54 3.77 23.35 10.71 1019.6 523 3.78 13 34.99 5.09 42.87 3.36 5.22 8.46 5.26 4.04 14 23 0.458.8 7.8 6.1 3.9 505 4.2

Glass frits useful in the present invention include ASF1100 and ASF1100Bwhich are commercially available from Asahi Glass Company. An averageparticle size of the glass frit (glass composition) in an embodiment ofthe present invention may be in the range of 0.5-1.5 μm. In a furtherembodiment, an average particle size may be in the range of 0.8-1.2 μm.In an embodiment, the softening point of the glass frit (T_(g): Secondtransition point of DTA) is in the range of 300-600° C. The T_(g) isdetermined by the intersection of the two extension lines drawn on theDTA plot for the specific material where the base line dips into anendotherm associated with the initiation of particle sintering. In anembodiment, the amount of glass frit in the total composition may be inthe range of 0.5 to 4 wt. % of the total composition. In one embodiment,the glass composition is present in the amount of 1 to 3 weight percenttotal composition. In a further embodiment, the glass composition ispresent in the range of 1.5 to 2.5 weight percent total composition.

The glasses described herein are produced by conventional glass makingtechniques. The glasses were prepared in 500-1000 gram quantities. Theingredients may be weighed and mixed in the desired proportions andheated in a bottom-loading furnace to form a melt in platinum alloycrucibles. As is well-known in the art, heating was conducted to a peaktemperature (1000° C.-1200° C.) and for a time such that the meltbecomes entirely liquid and homogeneous. The molten glass was quenchedbetween counter rotating stainless steel rollers to form a 10-20 milthick platelet of glass. The resulting glass platelet was then milled toform a powder with its 50% volume distribution set between 0.8-1.5microns.

The T_(g) data in Table 1 was derived from thermo-mechanic analysis(TMA) measurements using a TA instruments Q400 using a dynamic force of0.05 Newton on a pressed powder pellet 2.0-2.5 mm in thickness. Thesamples were heated at a rate of 10° C./min. from room temperature to atemperature where viscous flow is dominant in its thermal deformation.

In an embodiment, one or more additives described herein, such as ZnO,MgO, etc, may be contained in a glass. The glass frits which contain theone or more additives are useful in the embodiments described herein.

In an embodiment, the glass frit may include Bi₂O₃, B₂O₃ 8-25 weightpercent of total glass composition, and further comprises one or morecomponents selected from the group consisting of: SiO₂, P₂O₅, GeO₂, andV₂O₅.

In an embodiment, the glass frit may include one or more of Al₂O₃, CeO₂,SnO₂, and CaO. In an aspect of this embodiment, based on weight percentof total glass composition, the amount of Al₂O₃, CeO₂, SnO₂, and CaO maybe less than 6. In an aspect of this embodiment, based on weight percentof total glass composition, the amount of Al₂O₃, CeO₂, SnO₂, and CaO maybe less than 1.5.

In an embodiment, the glass frit may include one or more of BiF₃ andBi₂O₃. In an aspect of this embodiment, based on weight percent of totalglass composition, the amount of BiF₃ and Bi₂O₃ may be less than 83. Inan aspect of this embodiment, based on weight percent total of glasscomposition, the amount of BiF₃ and Bi₂O₃ may be less than 72.

In an embodiment, the glass frit may include one or more of Na₂O, Li₂O,and Ag₂O. In an aspect of this embodiment, based on weight percent oftotal glass composition, the amount of Na₂O, Li₂O, and Ag₂O may be lessthan 5. In an aspect of this embodiment, based on weight percent oftotal glass composition, the amount of Na₂O, Li₂O, and Ag₂O may be lessthan 2.0.

In an embodiment, the glass frit may include one or more of Al₂O₃,Si₂O₂, and B₂O₃. In an aspect of this embodiment, based on weightpercent of total glass composition, the amount of Si₂O₂, Al₂O₃, and B₂O₃may be less than 31.

In an embodiment, the glass frit may include one or more of Bi₂O₃, BiF₃,Na₂O, Li₂O, and Ag₂O. In an embodiment, based on weight percent of totalglass composition, the amount of (Bi₂O₃+BiF₃)/(Na₂O+Li₂O+Ag₂O) may begreater than 14.

As used herein, “lead-free” means that no lead has been added. In anembodiment, trace amounts of lead may be present in a composition andthe composition may still be considered lead-free if no lead was added.In an embodiment, a lead-free composition may contain less than 1000 ppmof lead. In an embodiment, a lead-free composition may contain less than300 ppm of lead. One of skill in the art will recognize thatcompositions containing lesser amounts of lead are encompassed by theterm lead-free. In an embodiment, a lead-free composition may not onlybe free of lead, but may also be free of other toxic materials,including Cd, Ni, and carcinogenic toxic materials, for example. In anembodiment, a lead-free composition may contain less than 1000 ppm oflead, less than 1000 ppm of Cd, and less than 1000 ppm of Ni. In anembodiment, the lead-free composition may contain trace amounts of Cdand/or Ni; in an embodiment, no Cd, Ni, or carcinogenic toxic materialsare added to a lead-free composition.

Flux Materials

An embodiment of the present invention relates to a thick filmcomposition, structures and devices including, and methods of making thestructures and devices, wherein the thick film includes flux materials.The flux materials, in an embodiment, may have properties similar to theglass materials, such as possessing lower softening characteristics. Forexample, compounds such as oxide or halogen compounds may be used. Thecompounds may assist penetration of an insulating layer in thestructures described herein. Non-limiting examples of such compoundsinclude materials that have been coated or encased in organic orinorganic barrier coating to protect against adverse reactions withorganic binder components of the paste medium. Non-limiting examples ofsuch flux materials may include PbF₂, BiF₃, V₂O₅, alkali metal oxidesand the like.

Glass Blending

In an embodiment, one or more glass frit materials may be present as anadmixture in the thick film composition. In an embodiment, a first glassfrit material may be selected by one of skill in the art for itscapability to rapidly digest the insulating layer; further the glassfrit material may have strong corrosive power and low viscosity.

In an embodiment, the second glass frit material may be designed toslowly blend with the first glass frit material while retarding thechemical activity. A stopping condition may result which may effect thepartial removal of the insulating layer but without attacking theunderlying emitter diffused region potentially shunting the device isthe corrosive action proceeds unchecked. Such a glass frit material maybe characterized as having a sufficiently higher viscosity to provide astable manufacturing window to remove insulating layers without damageto the diffused p-n junction region of the semiconductor substrate.

In a non-limiting exemplary admixture, the first glass frit material maybe SiO₂ 1.7 wt %, ZrO₂ 0.5 wt %, B₂O₃ 12 wt %, Na₂O 0.4 wt %, Li₃2O 0.8wt %, and Bi₂O₃ 84.6 wt % and the second glass frit material may be asSiO₂ 27 wt %, ZrO₂ 4.1 wt %, Bi₂O₃ 68.9 wt %. The proportions of theblend may be used to adjust the blend ratio to meet optimal performanceof the thick film conductor paste, under conditions recognized by one ofskill in the art.

Analytical Glass Testing

Several testing methods may be used to characterize glass materials ascandidates for application to photovoltaic Ag conductor formulation, andare recognized by one of skill in the art. Among these measurements areDifferential Thermal Analysis, DTA and Thermo-mechanical Analysis, TMAfor the determination of Tg and glass flow kinetics. As needed, manyadditional characterization methods may be employed such as dilatometry,thermogravimetric analysis, XRD, XRF, and ICP

Inert Gas Firing

In an embodiment, the processing of photovoltaic device cells utilizesnitrogen or other inert gas firing of the prepared cells. The firingtemperature profile is typically set so as to enable the burnout oforganic binder materials from dried thick film paste or other organicmaterials present. In an embodiment, the temperature may be between300-525 Celsius. The firing may be conducted in a belt furnace usinghigh transport rates, for example between 40-200 inches per minute.Multiple temperature zones may be used to control the desired thermalprofile. The number of zones may vary between 3 to 9 zones, for example.The photovoltaic cells may be fired at set temperatures between 650 and1000 C, for example. The firing is not limited to this type of firing,and other rapid fire furnace designs known to one of skill in the artare contemplated.

II. Organic Medium

The inorganic components may be mixed with an organic medium bymechanical mixing to form viscous compositions called “pastes”, havingsuitable consistency and rheology for printing. In an embodiment of theinvention, the organic medium may include one or more componentsselected from the group consisting of: Bis(2-(2Butoxyethoxy)Ethyl)Adipate, dibasic ester such as DBE, DBE-2, DBE-3, DBE-4, DBE-5, DBE-6,DBE-9, and DBE-IB, Octyl Epoxy Tallate [DRAPEX (R) 4.4] from WitcoChemical, and Oxocol (isotetradecanol made by Nissan Chemical) andForalyn™ 110 (pentaerythritol ester of hydrogenated rosin from EastmanChemical BV). In an embodiment of the invention, the organic medium mayinclude one or more components that burns out at temperatures above 400C, or, in a further embodiment, 500 C.

A wide variety of inert viscous materials can be included in the organicmedium. The organic medium may be one in which the inorganic componentsare dispersible with an adequate degree of stability. The rheologicalproperties of the medium lend good application properties to thecomposition, including: stable dispersion of solids, appropriateviscosity and thixotropy for screen printing, appropriate wettability ofthe substrate and the paste solids, a good drying rate, and good firingproperties. In an embodiment of the present invention, the organicvehicle used in the thick film composition of the present invention maybe a nonaqueous inert liquid. The organic medium presents in theconductive composition may be in the range of 10 wt % to 20 wt % of thetotal composition.

In an embodiment, the organic medium may include one or more additionalcomponents. In an aspect, the one or more additional components mayinclude one or more components selected from the group consisting of:Bis(2-(2Butoxyethoxy)Ethyl) Adipate, dibasic ester including DBE, DBE-2,DBE-3, DBE-4, DBE-5, DBE-6, DBE-9, DBE-IB, Octyl Epoxy Tallate [DRAPEX(R) 4.4] from Witco Chemical, and Oxocol (isotetradecanol made by NissanChemical) and Foralyn™ 110 (pentaerythritol ester of hydrogenated rosinfrom Eastman Chemical BV).

In an embodiment of the invention, the organic medium may include one ormore components that burn out at temperatures above 400 C, or, in afurther embodiment, 500 C.

Dibasic ester comprises one or more dimethyl ester selected from thegroup consisting of of dimethyl ester of adipic acid, dimethyl ester ofglutaric acid or dimethyl ester of succinic acid. Eight kinds of DBEfractions are available that differ in the amounts of each of threediesters of dimethyl adipate, dimethyl glutarate and dimethyl succinatepresent as shown in the table 2. Dibasic ester which is sold as DBE-3 ispreferred in this present invention. DBE-3 that material is said by itsmanufacturer to contain 85-95 weight percent dimethyl adipate, 5-15weight percent dimethyl glutarate and 0-1.0 weight percent dimethylsuccinate based on total weight of dibasic ester.

The above said one or more components selected from the group consistingof: Bis(2-(2Butoxyethoxy)Ethyl) Adipate, dibasic ester, Octyl EpoxyTallate [DRAPEX (R) 4.4], Oxocol and Foralyn™ 110 present in the organicmedium may be in the range of 1 wt % to 99.9 wt % of the organic medium.The minimum content is more preferably 10 wt % of the organic medium toobtain better electrical property in a solar cell. The minimum contentis further more preferably 30 wt %. The maximum content is morepreferably 95 wt % of the organic medium. The maximum content is furthermore preferably 90 wt %. Bis(2-(2Butoxyethoxy)Ethyl)Adipate, dibasicester, Octyl Epoxy Tallate and isotetradecanol have a function which isalmost equal to solvent. Therefore Bis(2-(2Butoxyethoxy)Ethyl) Adipate,dibasic ester, Octyl Epoxy Tallate and isotetradecanol may be replacedwith a part of or all of conventional solvent such as texanol in acomposition.

TABLE 2 DBE DBE-2 DBE-3 DBE-4 DBE-5 DBE-6 DBE-9 DBE-IB Ester content, 9999 99 98.5 99.5 99 99 98.5 wt. %, min. Water content, 0.1 0.1 0.2 0.040.1 0.05 0.1 0.2 wt. %, max. Acid number, 0.3 1 1 0.5 0.5 1 0.5 1 mgKOH/g, max. Dimethyl 10-25 20-28 85-95 0-0.1 0-0.2 98.5-100    0-0.310-25* adipate, wt % Dimethyl 55-65 72-78  5-15 0-0.4 98.5-100  0-1.065-69 55-70* glutarate, wt % Dimethyl 15-25   0-1.0   0-1.0 98-100 0-1.0  0-0.15 31-35 15-30* succinate, wt % *Di-isobutylester

The organic medium may contain one or more additional components, suchas, for example, thickeners, stabilizers, surfactants, viscositymodifier and/or polymers. Exemplary polymers include, but are notlimited to: ethyl cellulose, ethylhydroxyethyl cellulose, wood rosin,mixtures of ethyl cellulose and phenolic resins, polymethacrylates oflower alcohols, and monobutyl ether of ethylene glycol monoacetate.Exemplary solvents include, but are not limited to ester alcohols andterpenes such as alpha- or beta-terpineol or mixtures thereof with othersolvents such as kerosene, dibutylphthalate, butyl carbitol, butylcarbitol acetate, hexylene glycol and high boiling alcohols and alcoholesters. In addition, volatile liquids may be included in the vehicle.Various combinations of these and other solvents are formulated toobtain the viscosity and volatility requirements desired.

The polymer present in the organic medium may be in the range of 0.1 wt% to 6 wt % of the total composition. The thick film silver compositionof the present invention may be adjusted to a predetermined,screen-printable viscosity with the organic medium.

The ratio of organic medium in the thick film composition to theinorganic components in the dispersion is dependent on the method ofapplying the paste and the kind of organic medium used, and it can vary.Usually, the dispersion will contain 70-95 wt % of inorganic componentsand 5-30 wt % of organic medium (vehicle) in order to obtain goodwetting.

An embodiment of the present invention relates to a thick filmcomposition, wherein the thick film composition includes:

-   -   (a) an electrically conductive silver powder;    -   (b) one or more glass frits; dispersed in    -   (c) an organic medium, wherein the organic medium comprises one        or more components selected from the group consisting of:

Bis(2-(2Butoxyethoxy)Ethyl) Adipate, DBE, DBE-2, DBE-3, DBE-4, DBE-5,DBE-6, DBE-9, DBE-IB, Octyl Epoxy Tallate, and isotetradecanol andpentaerythritol ester of hydrogenated rosin.

In an aspect of this embodiment, the glass frit includes: Bi₂O₃ 28-85,B₂O₃ 8-25, and one or more of: SiO₂ 0-8, P₂O₅ 0-3, GeO₂ 0-3, V₂O₅ 0-3.In an aspect of this embodiment, the glass frit includes SiO₂ 0.1-8. Inan aspect of this embodiment, the glass frit may include one or moreintermediate oxides. Exemplary intermediate oxides include, but are notlimited to: Al₂O₃, CeO₂, SnO₂, TiO₂, Ta₂O₅, Nb₂O₅, and ZrO₂. In anaspect of this embodiment, the glass frit may include one or morealkaline earth constituents. Exemplary alkaline earth constituentsinclude, but are not limited to: CaO, SrO, BaO, MgO. In an embodiment,the glass frit may include one or more components selected from thegroup consisting of: ZnO, Na₂O, Li₂O, AgO₂, and BiF₃.

In an aspect of this embodiment, the composition may also include anadditive. Exemplary additives include: a metal additive, or ametal-containing additive, and wherein the metal additive ormetal-containing additive forms an oxide under processing conditions.The additive may be a metal oxide additive. For example, the additivemay be a metal oxide of one or more of the metals selected from Gd, Ce,Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu, and Cr.

An embodiment of the invention relates to a semiconductor deviceincluding the composition including:

-   -   (a) an electrically conductive silver powder;    -   (b) one or more glass frits; dispersed in    -   (c) an organic medium, wherein the organic medium comprises one        or more components selected from the group consisting of:        Bis(2-(2Butoxyethoxy)Ethyl) Adipate, DBE, DBE-2, DBE-3, DBE-4,        DBE-5, DBE-6, DBE-9, DBE-IB, Octyl Epoxy Tallate, and        isotetradecanol and pentaerythritol ester of hydrogenated rosin.

An embodiment of the invention relates to a structure including:

(a) the thick film composition including:

-   -   (a) an electrically conductive silver powder;    -   (b) one or more glass frits; dispersed in    -   (c) an organic medium, wherein the organic medium comprises one        or more components selected from the group consisting of:        Bis(2-(2Butoxyethoxy)Ethyl) Adipate, DBE, DBE-2, DBE-3, DBE-4,        DBE-5, DBE-6, DBE-9, DBE-IB, Octyl Epoxy Tallate, and        isotetradecanol and pentaerythritol ester of hydrogenated rosin.        (b) an insulating film        wherein the thick film composition is formed on the insulating        film, and wherein, upon firing, the insulating film is        penetrated by components of the thick film composition and the        organic medium is removed.        Structures

An embodiment of the present invention relates to structure including athick film composition and a substrate. In an embodiment, the substratemay be one or more insulating films. In an embodiment, the substrate maybe a semiconductor substrate. In an embodiment, the structures describedherein may be useful in the manufacture of photovoltaic devices. Anembodiment of the invention relates to a semiconductor device containingone or more structures described herein; an embodiment of the inventionrelates to a photovoltaic device containing one or more structuresdescribed herein; an embodiment of the invention relates to a solar cellcontaining one or more structures described herein; an embodiment of theinvention relates to a solar panel containing one or more structuresdescribed herein.

An embodiment of the present invention relates to an electrode formedfrom the thick film composition. In an embodiment, the thick filmcomposition has been fired to remove the organic vehicle and sinter thesilver and glass particles. An embodiment of the present inventionrelates to a semiconductor device containing an electrode formed fromthe thick film composition. In an embodiment, the electrode is a frontside electrode.

An embodiment of the present invention relates to structures describedherein, wherein the structures also include a back electrode.

An embodiment of the present invention relates to structures, whereinthe structures include thick film conductor compositions. In an aspect,the structure also includes one or more insulating films. In an aspect,the structure does not include an insulating film. In an aspect, thestructure includes a semiconductor substrate. In an aspect, the thickfilm conductor composition may be formed on the one or more insulatingfilms. In an aspect, the thick film conductor composition may be formedon the semiconductor substrate. In the aspect wherein the thick filmconductor composition may be formed on the semiconductor substrate, thestructure may not contain an insulating film.

Thick Film Conductor and Insulating Film Structure

An aspect of the present invention relates to a structure including athick film conductor composition and one or more insulating films. Thethick film composition may include: (a) an electrically conductivesilver powder; (b) one or more glass frits; dispersed in c) an organicmedium, wherein the organic medium comprises one or more componentsselected from the group consisting of: Bis(2-(2Butoxyethoxy)Ethyl)Adipate, DBE, DBE-2, DBE-3, DBE-4, DBE-5, DBE-6, DBE-9, DBE-IB, OctylEpoxy Tallate, and isotetradecanol and pentaerythritol ester ofhydrogenated rosin. In an embodiment, the glass frits may be lead-free.In an embodiment, the thick film composition may also include anadditive, as described herein. The structure may also include asemiconductor substrate. In an embodiment of the invention, upon firing,the organic vehicle may be removed and the silver and glass frits may besintered. In a further aspect of this embodiment, upon firing, theconductive silver and frit mixture may penetrate the insulating film.

The thick film conductor composition may penetrate the insulating filmupon firing. The penetration may be partial penetration. The penetrationof the insulating film by the thick film conductor composition mayresult in an electrical contact between the conductor of the thick filmcomposition and the semiconductor substrate.

The thick film conductor composition may be printed on the insulatingfilm in a pattern. The printing may result in the formation of busbarswith connecting lines, as described herein, for example.

The printing of the thick film may be by plating, extrusion, inkjet,shaped or multiple printing, or ribbons, for example.

A layer of silicon nitride may be present on the insulating film. Thesilicon nitride may be chemically deposited. The deposition method maybe CVD, PCVD, or other methods known to one of skill in the art.

Insulating Films

In an embodiment of the invention, the insulating film may include oneor more component selected from: titanium oxide, silicon nitride,SiNx:H, silicon oxide, and silicon oxide/titanium oxide. In anembodiment of the invention, the insulating film may be ananti-reflection coating (ARC). In an embodiment of the invention, theinsulating film may be applied; the insulating film may be applied to asemiconductor substrate. In an embodiment of the invention, theinsulting film may be naturally forming, such as in the case of siliconoxide. In an embodiment, the structure may not include an insulatingfilm that has been applied, but may contain a naturally formingsubstance, such as silicon oxide, which may function as an insulatingfilm.

Thick Film Conductor and Semiconductor Substrate Structure

An aspect of the present invention relates to a structure including athick film conductor composition and a semiconductor substrate. In anembodiment, the structure may not include an insulating film. In anembodiment, the structure may not include an insulating film which hasbeen applied to the semiconductor substrate. In an embodiment, thesurface of the semiconductor substrate may include a naturally occurringsubstance, such as SiO₂. In an aspect of this embodiment, the naturallyoccurring substance, such as SiO₂, may have insulating properties.

The thick film conductor composition may be printed on the semiconductorsubstrate in a pattern. The printing may result in the formation ofbusbars with connecting lines, as described herein, for example. Anelectrical contact may be formed between the conductor of the thick filmcomposition and the semiconductor substrate.

A layer of silicon nitride may be present on the semiconductorsubstrate. The silicon nitride may be chemically deposited. Thedeposition method may be CVD, PCVD, or other methods known to one ofskill in the art.

Structure in Which the Silicon Nitride may be Chemically Treated

An embodiment of the invention relates to a structure in which thesilicon nitride of the insulating layer may be treated resulting in theremoval of at least a portion of the silicon nitride. The treatment maybe chemical treatment. The removal of at least a portion of the siliconnitride may result in an improved electrical contact between theconductor of the thick film composition and the semiconductor substrate.The structure may have improved efficiency.

In an aspect of this embodiment, the silicon nitride of the insulatingfilm may be part of the anti-reflective coating (ARC). The siliconnitride may be naturally forming, or chemically deposited, for example.The chemical deposition may be by CVD or PCVD, for example.

Structure in which the Thick Film Composition Includes Flux Materialsthat are not Glass Frit

An embodiment of the invention relates to a structure including a thickfilm composition and one or more insulating films, in which the thickfilm composition includes an electrically conductive silver powder, oneor more flux materials, and an organic medium, and wherein the structurefurther comprises one or more insulating films. In an aspect of thisembodiment, the flux materials are lead-free. In an aspect, the fluxmaterials are not glass frit. In an embodiment, the structure mayfurther include a semiconductor substrate.

The thick film conductor composition may penetrate the insulating filmupon firing. The penetration may be partial penetration. For example, apercentage of the surface of the insulating film may be penetrated bythe thick film conductor composition. The penetration of the insulatingfilm by the thick film conductor composition may result in an electricalcontact between the conductor of the thick film composition and thesemiconductor substrate.

In an embodiment of the present invention, a method and structure areprovided in which a conductor has been applied directly to thesemiconductor substrate. In an aspect of this embodiment, a mask mayhave been applied to the semiconductor substrate in a patterncorrelating to the pattern of the conductor. An insulating may have thenbeen applied, with subsequent removal of the mask. The conductorcomposition may have then been applied to the semiconductor substrate ina pattern correlating to the area from which the mask was removed.

An embodiment of the present invention relates to a semiconductor devicewhich includes a composition, wherein, prior to firing, the compositionincludes:

-   an electrically conductive silver powder;-   one or more glass frits wherein said glass frits are lead-free;    dispersed in an organic medium.

In an aspect of this embodiment, the composition may include anadditive. Exemplary additives are described herein. An aspect of thisembodiment relates to a solar cell including the semiconductor device.An aspect of this embodiment relates to a solar panel including thesolar cell.

Busbars

In an embodiment, the thick film conductor composition may be printed onthe substrate to form busbars. The busbars may be more than two busbars.For example, the busbars may be three or more busbars. In addition tobusbars, the thick film conductor composition may be printed on thesubstrate to form connecting lines. The connecting lines may contact abusbar. The connecting lines contacting a busbar may be interdigitatedbetween the connecting lines contacting a second busbar.

In an exemplary embodiment, three busbars may be parallel to each otheron a substrate. The busbars may be rectangular in shape. Each of thelonger sides of the middle busbar may be in contact with connectinglines. On each of the side busbars, only one side of the longerrectangle may be in contact with connecting lines. The connecting linescontacting the side busbars may interdigitate with the connecting linescontacting the middle busbar. For example, the connecting linescontacting one side busbar may interdigitate with the connecting linescontacting the middle busbar on one side, and the connecting linescontacting the other side busbar may interdigitate with the connectinglines contacting the middle busbar on the other side of the middlebusbar.

FIG. 2A provides an exemplary representation of an embodiment in whichthere are two busbars. A first busbar 201 is in contact with a first setof connecting lines 203. A second busbar 205 is in contact with a secondset of connecting lines 207. The first set of connecting lines 203interdigitate with the second set of connecting lines 207.

FIG. 2B provides an exemplary representation of an embodiment in whichthere are three busbars. A first busbar 209 is in contact with a firstset of connecting lines 211. A second busbar 213 is in contact with botha second set of connecting lines 215 and a third set of connecting lines217. The second set of connecting lines 215 contacts one side of thesecond busbar 213; the third set of connecting lines 217 contacts theopposite side of the second busbar 213. A third busbar 219 is in contactwith a fourth set of connecting lines 221. The first set of connectinglines 211 interdigitate with the second set of connecting lines 215. Thethird set of connecting lines 217 interdigitate with the fourth set ofconnecting lines 221.

Description of Method of Manufacturing a Semiconductor Device

An embodiment of the invention relates to a method of manufacturing asemiconductor device. An aspect of this embodiment includes the stepsof:

-   (a) providing a semiconductor substrate, one or more insulating    films, and a thick film composition, wherein the thick film    composition comprises: a) an electrically conductive silver    powder, b) one or more glass frits, dispersed in c) an organic    medium, wherein the organic medium comprises one or more components    selected from the group consisting of: Bis(2-(2Butoxyethoxy)Ethyl)    Adipate, DBE, DBE-2, DBE-3, DBE-4, DBE-5, DBE-6, DBE-9, DBE-IB,    Octyl Epoxy Tallate, and isotetradecanol and pentaerythritol ester    of hydrogenated rosin.-   (b) applying one or more insulating films on the semiconductor    substrate,-   (c) applying the thick film composition on the one or more    insulating films on the semiconductor substrate, and-   (d) firing the semiconductor, one or more insulating films and thick    film composition,    wherein, upon firing, the organic vehicle is removed, the silver and    glass frits are sintered, and the insulating film is penetrated by    components of the thick film composition.

In an aspect of this embodiment, the glass frits may be lead-free. In anaspect of this embodiment, the one or more insulating films may beselected from the group including: silicon nitride film, titanium oxidefilm, SiNx:H film, silicon oxide film and a silicon oxide/titanium oxidefilm.

An embodiment of the invention relates to semiconductor device formed bya method described herein. An embodiment of the invention relates to asolar cell including a semiconductor device formed by a method describedherein. An embodiment of the invention relates to a solar cell includingan electrode, which includes a silver powder and one or more glassfrits, wherein the glass frits are lead-free.

An embodiment of the present invention provides a novel composition(s)that may be utilized in the manufacture of a semiconductor device. Thesemiconductor device may be manufactured by the following method from astructural element composed of a junction-bearing semiconductorsubstrate and a silicon nitride insulating film formed on a main surfacethereof. The method of manufacture of a semiconductor device includesthe steps of applying (for example, coating and printing) onto theinsulating film, in a predetermined shape and at a predeterminedposition, the conductive thick film composition of the present inventionhaving the ability to penetrate the insulating film, then firing so thatthe conductive thick film composition melts and passes through theinsulating film, effecting electrical contact with the siliconsubstrate. In an embodiment, the electrically conductive thick filmcomposition may be a thick-film paste composition, as described herein,which is made of a silver powder, Zn-containing additive, a glass orglass powder mixture having a softening point of 300 to 600° C.,dispersed in an organic vehicle and optionally, additional metal/metaloxide additive(s).

In an embodiment, the composition may include a glass powder content ofless than 5% by weight of the total composition and a Zn-containingadditive combined with optional additional metal/metal oxide additivecontent of no more than 6% by weight of the total composition. Anembodiment of the invention also provides a semiconductor devicemanufactured from the same method.

In an embodiment of the invention, silicon nitride film or silicon oxidefilm may be used as the insulating film. The silicon nitride film may beformed by a plasma chemical vapor deposition (CVD) or thermal CVDprocess. In an embodiment, the silicon oxide film may be formed bythermal oxidation, thermal CFD or plasma CFD.

In an embodiment, the method of manufacture of the semiconductor devicemay also be characterized by manufacturing a semiconductor device from astructural element composed of a junction-bearing semiconductorsubstrate and an insulating film formed on one main surface thereof,wherein the insulating layer is selected from a titanium oxide siliconnitride, SiNx:H, silicon oxide, and silicon oxide/titanium oxide film,which method includes the steps of forming on the insulating film, in apredetermined shape and at a predetermined position, a metal pastematerial having the ability to react and penetrate the insulating film,forming electrical contact with the silicon substrate. The titaniumoxide film may be formed by coating a titanium-containing organic liquidmaterial onto the semiconductor substrate and firing, or by a thermalCVD. In an embodiment, the silicon nitride film may be formed by PECVD(plasma enhanced chemical vapor deposition). An embodiment of theinvention also provides a semiconductor device manufactured from thissame method.

In an embodiment of the invention, the electrode formed from theconductive thick film composition(s) of the present invention may befired in an atmosphere composed of a mixed gas of oxygen and nitrogen.This firing process removes the organic medium and sinters the glassfrit with the Ag powder in the conductive thick film composition. Thesemiconductor substrate may be single-crystal or multicrystallinesilicon, for example.

FIG. 1( a) shows a step in which a substrate is provided, with atextured surface which reduces light reflection. In an embodiment, asemiconductor substrate of single-crystal silicon or of multicrystallinesilicon is provided. In the case of solar cells, substrates may besliced from ingots which have been formed from pulling or castingprocesses. Substrate surface damage caused by tools such as a wire sawused for slicing and contamination from the wafer slicing step may beremoved by etching away about 10 to 20 μm of the substrate surface usingan aqueous alkali solution such as aqueous potassium hydroxide oraqueous sodium hydroxide, or using a mixture of hydrofluoric acid andnitric acid. In addition, a step in which the substrate is washed with amixture of hydrochloric acid and hydrogen peroxide may be added toremove heavy metals such as iron adhering to the substrate surface. Anantireflective textured surface is sometimes formed thereafter using,for example, an aqueous alkali solution such as aqueous potassiumhydroxide or aqueous sodium hydroxide. This gives the substrate, 10.

Next, referring to FIG. 1( b), when the substrate used is a p-typesubstrate, an n-type layer is formed to create a p-n junction. Themethod used to form such an n-type layer may be phosphorus (P) diffusionusing phosphorus oxychloride (POCl₃). The depth of the diffusion layerin this case can be varied by controlling the diffusion temperature andtime, and is generally formed within a thickness range of about 0.3 to0.5 μm. The n-type layer formed in this way is represented in thediagram by reference numeral 20. Next, p-n separation on the front andbacksides may be carried out by the method described in the backgroundof the invention. These steps are not always necessary when aphosphorus-containing liquid coating material such as phosphosilicateglass (PSG) is applied onto only one surface of the substrate by aprocess, such as spin coating, and diffusion is effected by annealingunder suitable conditions. Of course, where there is a risk of an n-typelayer forming on the backside of the substrate as well, the degree ofcompleteness can be increased by employing the steps detailed in thebackground of the invention.

Next, in FIG. 1( d), a silicon nitride film or other insulating filmsincluding SiNx:H (i.e., the insulating film comprises hydrogen forpassivation during subsequent firing processing) film, titanium oxidefilm, and silicon oxide film, 30, which functions as an antireflectioncoating is formed on the above-described n-type diffusion layer, 20.This silicon nitride film, 30, lowers the surface reflectance of thesolar cell to incident light, making it possible to greatly increase theelectrical current generated. The thickness of the silicon nitride film,30, depends on its refractive index, although a thickness of about 700to 900 Å is suitable for a refractive index of about 1.9 to 2.0. Thissilicon nitride film may be formed by a process such as low-pressureCVD, plasma CVD, or thermal CVD. When thermal CVD is used, the startingmaterials are often dichlorosilane (SiCl₂H₂) and ammonia (NH₃) gas, andfilm formation is carried out at a temperature of at least 700° C. Whenthermal CVD is used, pyrolysis of the starting gases at the hightemperature results in the presence of substantially no hydrogen in thesilicon nitride film, giving a compositional ratio between the siliconand the nitrogen of Si₃N₄ which is substantially stoichiometric. Therefractive index falls within a range of substantially 1.96 to 1.98.Hence, this type of silicon nitride film is a very dense film whosecharacteristics, such as thickness and refractive index, remainunchanged even when subjected to heat treatment in a later step. Thestarting gas used when film formation is carried out by plasma CVD isgenerally a gas mixture of SiH₄ and NH₃. The starting gas is decomposedby the plasma, and film formation is carried out at a temperature of 300to 550° C. Because film formation by such a plasma CVD process iscarried out at a lower temperature than thermal CVD, the hydrogen in thestarting gas is present as well in the resulting silicon nitride film.Also, because gas decomposition is effected by a plasma, anotherdistinctive feature of this process is the ability to greatly vary thecompositional ratio between the silicon and nitrogen. Specifically, byvarying such conditions as the flow rate ratio of the starting gases andthe pressure and temperature during film formation, silicon nitridefilms can be formed at varying compositional ratios between silicon,nitrogen and hydrogen, and within a refractive index range of 1.8 to2.5. When a film having such properties is heat-treated in a subsequentstep, the refractive index may change before and after film formationdue to such effects as hydrogen elimination in the electrode firingstep. In such cases, the silicon nitride film required in a solar cellcan be obtained by selecting the film-forming conditions after firsttaking into account the changes in film qualities that will occur as aresult of heat treatment in the subsequent step.

In FIG. 1( d), a titanium oxide film may be formed on the n-typediffusion layer, 20, instead of the silicon nitride film, 30,functioning as an antireflection coating. The titanium oxide film isformed by coating a titanium-containing organic liquid material onto then-type diffusion layer, 20, and firing, or by thermal CVD. It is alsopossible, in FIG. 1( d), to form a silicon oxide film on the n-typediffusion layer, 20, instead of the silicon nitride film 30 functioningas an antireflection layer. The silicon oxide film is formed by thermaloxidation, thermal CVD or plasma CVD.

Next, electrodes are formed by steps similar to those shown in FIGS. 1(e) and (f). That is, as shown in FIG. 1( e), aluminum paste, 60, andback side silver paste, 70, are screen printed onto the back side of thesubstrate, 10, as shown in FIG. 1( e) and successively dried. Inaddition, a front electrode-forming silver paste is screen printed ontothe silicon nitride film, 30, in the same way as on the back side of thesubstrate, 10, following which drying and firing are carried out in aninfrared furnace; the set point temperature range may be 700 to 975° C.for a period of from one minute to more than ten minutes while a mixedgas stream of oxygen and nitrogen are passed through the furnace.

As shown in FIG. 1( f), during firing, aluminum diffuses as an impurityfrom the aluminum paste into the silicon substrate, 10, on the backside, thereby forming a p+ layer, 40, containing a high aluminum dopantconcentration. Firing converts the dried aluminum paste, 60, to analuminum back electrode, 61. The backside silver paste, 70, is fired atthe same time, becoming a silver back electrode, 71. During firing, theboundary between the backside aluminum and the backside silver assumesthe state of an alloy, thereby achieving electrical connection. Mostareas of the back electrode are occupied by the aluminum electrode,partly on account of the need to form a p+ layer, 40. The silver orsilver/aluminum back electrode is formed on limited areas of thebackside as an electrode for interconnecting solar cells by means ofcopper ribbon or the like.

On the front side, the front electrode silver paste, 500, of theinvention is composed of silver, Zn-containing additive, glass frit,organic medium and optional metal oxides, and is capable of reacting andpenetrating through the silicon nitride film, 30, during firing toachieve electrical contact with the n-type layer, 20 (fire through).This fired-through state, i.e., the extent to which the front electrodesilver paste melts and passes through the silicon nitride film, 30,depends on the quality and thickness of the silicon nitride film, 30,the composition of the front electrode silver paste, and on the firingconditions. The conversion efficiency and moisture resistancereliability of the solar cell clearly depend, to a large degree, on thisfired-through state.

EXAMPLES

The thick film composition(s) of the present invention are describedherein below in Table 3-8.

Paste Preparation

Paste preparations were, in general, accomplished with the followingprocedure: The appropriate amount of solvent, medium and surfactant wasweighed then mixed in a mixing can for 15 minutes, then glass frits andmetal additives were added and mixed for another 15 minutes. Since Ag isthe major part of the solids of the present invention, it was addedincrementally to ensure better wetting. When well mixed, the paste wasrepeatedly passed through a 3-roll mill for at progressively increasingpressures from 0 to 400 psi. The gap of the rolls was adjusted to 1 mil.The degree of dispersion was measured by fineness of grind (FOG). TheFOG value may be equal to or less than 20/10 for conductors.

The ASF1100 glass frit (available from Asahi Glass Company) used in thefollowing examples was not used as supplied. It was milled to a D₅₀ inthe range of 0.5-0.7 microns prior to use.

Test Procedure-Efficiency

The solar cells built according to the method described above wereplaced in a EETS (Energy Equipment Testing Service Ltd, Cardiff, UK)PVcell tester 200 for measuring efficiencies. The Xe Arc lamp in the PVcell tester simulated the sunlight with a known intensity and radiatedthe front surface of the cell. The tester used a four contact method tomeasure current (I) and voltage (V) at approximately 400 load resistancesettings to determine the cell's I-V curve. Both fill factor (FF) andefficiency (Eff) were calculated from the I-V curve.

Paste efficiency and fill factor values were normalized to correspondingvalues obtained with cells contacted with industry standard.

Vehicle Design

A range of vehicles comprising different mixtures of resins and solventsas described herein were tested in the thick film compositions togetherwith a standard set of solids systems (comprising silver powders andinorganic constituents known in the art to provide good electricalproperties in silicon solar cells employing a silicon nitride basedanti-reflection coating).

Accordingly, the base compositions are described in Tables 3-6 asvehicle A, B, C, D, E and F comprising mixtures of solvents and resinsused in the art. For each vehicle and standard solids systems theexamples show additives selected from the group consisting of:

-   Bis(2-(2Butoxyethoxy)Ethyl) Adipate,-   DBE-3 Dibasic Ester (which is 85-95% dimethyl adipate and 5-15%    dimethyl glutarate from Invista),-   Octyl Epoxy Tallate [DRAPEX (R) 4.4] from Witco Chemical,-   and Oxocol (isotetradecanol made by Nissan Chemical),    which were added at two addition levels for each of the vehicles of    1% and 2%. The addition of Foralyn™ 110 (pentaerythritol ester of    hydrogenated rosin from Eastman Chemical BV) was undertaken at one    level of 1.25%.

Vehicle B with additives making up compositions B1 to B9 were screenprinted on a 157×157 mm multicrystalline wafer using a 200 micron wideline cell pattern designed to be compatible with 65 ohm/square emitters.The wafers were coated with a silicon nitride anti-reflection coatingdesigned to make a solar cell. DuPont PV381 aluminum paste was used as ap-type conductor and PV502 as the rear surface tabbing silvercomposition. The cells were fired in a 4 zone Centrotherm furnace withpeak temperature of 925 C. Cells were measured electrically under 1 sunconditions.

The efficiency distribution and mean of 5 cells for samples B1 to B9 isshown in FIG. 3 and clearly demonstrates an increase in performance forall of the additives in these experiments of plus 0.6% between A0 andB9. The pastes B7 and B9 were printed on the same material set of wafersusing 100 um pattern and the results are shown in FIG. 4, where weachieved a +1.1% efficiency increase over the base system, A0.

FIG. 5 shows the impact of the vehicle in combination with the selectedadditives

TABLE 3 A Vehicle A with addition matrix Ingredients A0 A1 A2 A3 A4 A5A6 A7 A8 A9 Vehicle A 12.10 12.10 11.10 10.10 11.10 10.10 11.10 10.1011.10 10.10 Vehicle B Vehicle C Vehicle D Vehicle E Vehicle F Basesolids 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90Vehicle Additions Foralyn 110 ETHYL 3-ETHOXYPROPIONATE 1.00 ETHYL3-ETHOXYPROPIONATE 2.00 FINE OXOCOL-140N 1.00 FINE OXOCOL-140N 2.00BIS(2-(2-BUTOXYETHOXY) ETHYL) 1.00 ADIPATE BIS(2-(2-BUTOXYETHOXY) ETHYL)2.00 ADIPATE DBE-3 DIBASIC ESTER (Mixture of 1.00 DIMTHYL ADIPATE andDIMETHYL GLUTARATE) DBE-3 DIBASIC ESTER (Mixture of 2.00 DIMTHYL ADIPATEand DIMETHYL GLUTARATE) total 100.00 100.00 100.00 100.00 100.00 100.00100.00 100.00 100.00 100.00

TABLE 4 A Vehicle B with addition matrix Ingredients A0 B1 B2 B3 B4 B5B6 B7 B8 B9 Vehicle A 12.10 Vehicle B 10.85 9.85 8.85 9.85 8.85 9.858.85 9.85 8.85 Vehicle C Vehicle D Vehicle E Vehicle F Base solids 87.9087.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 Vehicle AdditionsForalyn 110 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 ETHYL3-ETHOXYPROPIONATE 1.00 ETHYL 3-ETHOXYPROPIONATE 2.00 FINE OXOCOL-140N1.00 FINE OXOCOL-140N 2.00 BIS(2-(2-BUTOXYETHOXY) ETHYL) 1.00 ADIPATEBIS(2-(2-BUTOXYETHOXY) ETHYL) 2.00 ADIPATE DBE-3 DIBASIC ESTER (Mixtureof 1.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) DBE-3 DIBASIC ESTER(Mixture of 2.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) total 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 5 A Vehicle C with addition matrix Ingredients A0 C1 C2 C3 C4 C5C6 C7 C8 C9 Vehicle A 12.10 Vehicle B Vehicle C 10.85 9.85 8.85 9.858.85 9.85 8.85 9.85 8.85 Vehicle D Vehicle E Vehicle F Base solids 87.9087.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 Vehicle AdditionsForalyn 110 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 ETHYL3-ETHOXYPROPIONATE 1.00 ETHYL 3-ETHOXYPROPIONATE 2.00 FINE OXOCOL-140N1.00 FINE OXOCOL-140N 2.00 BIS(2-(2-BUTOXYETHOXY) ETHYL) 1.00 ADIPATEBIS(2-(2-BUTOXYETHOXY) ETHYL) 2.00 ADIPATE DBE-3 DIBASIC ESTER (Mixtureof 1.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) DBE-3 DIBASIC ESTER(Mixture of 2.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) total 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 6 A Vehicle D with addition matrix Ingredients A0 D1 D2 D3 D4 D5D6 D7 D8 D9 Vehicle A 12.10 Vehicle B Vehicle C Vehicle D 10.85 9.858.85 9.85 8.85 9.85 8.85 9.85 8.85 Vehicle E Vehicle F Base solids 87.9087.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 Vehicle AdditionsForalyn 110 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 ETHYL3-ETHOXYPROPIONATE 1.00 ETHYL 3-ETHOXYPROPIONATE 2.00 FINE OXOCOL-140N1.00 FINE OXOCOL-140N 2.00 BIS(2-(2-BUTOXYETHOXY) ETHYL) 1.00 ADIPATEBIS(2-(2-BUTOXYETHOXY) ETHYL) 2.00 ADIPATE DBE-3 DIBASIC ESTER (Mixtureof 1.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) DBE-3 DIBASIC ESTER(Mixture of 2.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) total 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 7 A Vehicle E with addition matrix Ingredients A0 E1 E2 E3 E4 E5E6 E7 E8 E9 Vehicle A 12.10 Vehicle B Vehicle C Vehicle D Vehicle E10.85 9.85 8.85 9.85 8.85 9.85 8.85 9.85 8.85 Vehicle F Base solids87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 VehicleAdditions Foralyn 110 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 ETHYL3-ETHOXYPROPIONATE 1.00 ETHYL 3-ETHOXYPROPIONATE 2.00 FINE OXOCOL-140N1.00 FINE OXOCOL-140N 2.00 BIS(2-(2-BUTOXYETHOXY) ETHYL) 1.00 ADIPATEBIS(2-(2-BUTOXYETHOXY) ETHYL) 2.00 ADIPATE DBE-3 DIBASIC ESTER (Mixtureof 1.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) DBE-3 DIBASIC ESTER(Mixture of 2.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) total 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE 8 A Vehicle F with addition matrix Ingredients A0 F1 F2 F3 F4 F5F6 F7 F8 F9 Vehicle A 12.10 Vehicle B Vehicle C Vehicle D Vehicle EVehicle F 10.85 9.85 8.85 9.85 8.85 9.85 8.85 9.85 8.85 Base solids87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 87.90 VehicleAdditions Foralyn 110 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 ETHYL3-ETHOXYPROPIONATE 1.00 ETHYL 3-ETHOXYPROPIONATE 2.00 FINE OXOCOL-140N1.00 FINE OXOCOL-140N 2.00 BIS(2-(2-BUTOXYETHOXY) ETHYL) 1.00 ADIPATEBIS(2-(2-BUTOXYETHOXY) ETHYL) 2.00 ADIPATE DBE-3 DIBASIC ESTER (Mixtureof 1.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) DBE-3 DIBASIC ESTER(Mixture of 2.00 DIMTHYL ADIPATE and DIMETHYL GLUTARATE) total 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

In the next, electrical generating property of solar cell substrateswith electrodes made with conductive pastes containing dibasic esterwere measured. The amount of dibasic ester changed here.

Paste Preparation

Used material in the paste preparation is as follows. The content ofeach material is shown in Table 9.

Electrically functional conductive powder: A mixture of 76% of sphericalsilver powder [d₅₀ 1.7-2.8 μm as determined with a laser scattering-typeparticle size distribution measuring apparatus] was used.

Glass Frit: Bismuth-borosilicate glass frit was used. The content of thetotal glass frits was 3.2 wt % of the conductive paste.

Organic Medium: An organic medium consisting of Ethyl cellulose resin,dibasic ester (DBE-3, INVISTA Inc.) and Texanol were used as shown inTable 9. Moreover, 1.6 wt % of viscosity modifier was added to theorganic medium.

Additive: every conductive paste contained 3.7 wt % of ZnO as anadditive.

Paste preparations were, in general, accomplished with the followingprocedure: The appropriate amount of Ethyl cellulose resin, dibasicester (DBE-3, INVISTA Inc.) and Texanol described above were weighedthen mixed in a mixing can for 15 minutes, then silver powder and glassfrits described above and ZnO were added and mixed for another 5minutes. When well mixed, the paste was repeatedly passed through a3-roll mill for at progressively increasing pressures from 0 to 400 psi.The gap of the rolls was adjusted to 1 mm. The degree of dispersion wasmeasured by fineness of grind (FOG). A typical FOG value is generallyequal to or less than 20/10 for conductors.

TABLE 9 Composition Comparative Example Example Example Example Exampleexample 1 1 2 3 4 5 Ag 76 76 76 76 76 76 Glass 3.2 3.2 3.2 3.2 3.2 3.2ZnO 3.7 3.7 3.7 3.7 3.7 3.7 Organic medium Ethyl cellulose 2.3 2.3 2.42.4 2.5 0.4 Viscosity modifier 1.6 1.6 1.6 1.6 1.6 1.6 DBE-3 0.0 0.9 1.82.7 3.6 14.7 TEXANOL 13.1 12.1 11.2 10.3 9.4 0.0 DBE-3/Organic 0.00 0.050.11 0.16 0.21 0.88 medium ratioMethod of Electrode Production

Solar cells were formed by using the four kinds of conductive pastedescribed in (A) above. Firstly, silicone (Si) wafers (38 mm square and0.2 mm thickness) were prepared. Aluminum paste (PV322 E.I. du Pont deNemours and Company) were screen printed on the back side of these Siwafers and then dried at the temperature of 150° C. for 5 minutes. Theprinted pattern of aluminum paste was 34 mm×34 mm and 25 μm thicknessafter drying. The Ag paste was printed on front side of the Si wafer toform electrode pattern with a bus bar and fourteen finger lines at bothside of the bus bar. The wafers with printed pattern were dried under150° C. for 5 min. The dried pattern was fired in an IR heating beltfurnace in air. The maximum set temperature was 980° C. and its In-Outtime was 120 sec. The bus bar had 2 mm width and 15 μm thickness, andthe finger lines had 150 μm width and 15 μm thickness after firing.

Test Procedure of FF

The electrical characteristics (I-V characteristics) of the resultingsolar cell substrate of comparative example 1 and example 1-5 wereevaluated using a model NCT-M-150AA cell tester manufactured by NPC Co.Current-voltage curve (I-V curve) was made with the results of themeasurement to calculate Fill factor (FF value). In general, the higherFF value indicates the better electrical generation property in a solarcell.

Results

Example 1-5 obtained the higher FF value than comparative example.Stated another way, it could be said that replacing a part of or all ofconventional solvent with dibasic ester, the electrical generationproperty of a solar cell got better. And it was also seen that the moreamount of dibasic ester had been put in the composition, the higher FFvalue was obtained.

TABLE 10 Comparative Example Example Example Example Example example 1 12 3 4 5 0.725 0.740 0.745 0.744 0.750 0.76

1. A thick film conductive composition comprising: a) one or moreelectrically conductive powders; b) one or more glass frits, wherein theT_(g) of the one or more glass frits is 300-600° C., as measured byDifferential Thermal Analysis; c) a ZnO additive; and d) an organicmedium, wherein the organic medium comprises ethyl cellulose and one ormore components selected from the group consisting of:Bis(2-(2Butoxyethoxy)Ethyl)Adipate, dibasic ester, Octyl Epoxy Tallate,isotetradecanol, and pentaerythritol ester of hydrogenated rosin,wherein the ZnO additive is in addition to any ZnO present in the one ormore glass frits.
 2. The thick film conductive composition of claim 1,wherein the component is dibasic ester.
 3. The thick film conductivecomposition according to claim 2, wherein the dibasic ester comprisesone or more compounds selected from the group consisting of dimethylester of adipic acid, dimethyl ester of glutaric acid, and dimethylester of succinic acid.
 4. The thick film conductive compositionaccording to claim 1, wherein the one or more glass frits comprise,based upon weight percent of the total glass composition: SiO₂ 1-36,Al₂O₃ 0-7, B₂O₃ 1.5-19, PbO 20-83, ZnO 0-42, CuO 0-4, Bi₂O₃ 0-35, ZrO₂0-8, TiO₂ 0-7, PbF₂ 3-34.
 5. A structure comprising the thick filmcomposition of claim 1 on a substrate.
 6. The structure of claim 5wherein the substrate comprises one or more insulating layers.
 7. Thesubstrate of claim 5 comprising one or more semiconductor substrates. 8.An electrode of a solar cell, formed by applying a thick film conductivecomposition of claim 1 onto a substrate of the solar cell; and firingthe applied thick film conductive composition.
 9. A method ofmanufacturing a semiconductor device comprising: a) providing one ormore semiconductor substrates, one or more insulating films, and a thickfilm composition, wherein the thick film composition comprises: i) oneor more electrically conductive powders, ii) one or more glass frits,wherein the T_(g) of the one or more glass frits is 300-600° C., asmeasured by Differential Thermal Analysis; iii) a ZnO additive; and iv)an organic medium, wherein the organic medium comprises ethyl celluloseand one or more components selected from the group consisting of:Bis(2-(2Butoxyethoxy)Ethyl)Adipate, dibasic ester, Octyl Epoxy Tallate,isotetradecanol, and pentaerythritol ester of hydrogenated rosin,wherein the ZnO additive is in addition to any ZnO present in the one ormore glass frits, b) applying the insulating film on the semiconductorsubstrate; c) applying the thick film composition on the insulating filmon the semiconductor substrate; and d) firing the semiconductor,insulating film and thick film composition.
 10. The method of claim 9wherein the insulating film comprises one or more components selectedfrom: titanium oxide, silicon nitride, SiNx:H, silicon oxide, andsilicon oxide/titanium oxide.
 11. A thick film conductive compositioncomprising: a) one or more electrically conductive silver powders; b)one or more glass frits wherein the T_(g) of the one or more glass fritsis 300-600° C., as measured by Differential Thermal Analysis; c) a ZnOadditive; and d) an organic medium, wherein the organic medium comprisesethyl cellulose and dibasic ester, wherein the ZnO additive is inaddition to any ZnO present in the one or more glass frits.
 12. Thethick film conductive composition according to claim 11, wherein thedibasic ester comprises one or more compounds selected from the groupconsisting of dimethyl ester of adipic acid, dimethyl ester of glutaricacid, and dimethyl ester of succinic acid.